Journal
AMERICAN JOURNAL OF RESPIRATORY CELL AND MOLECULAR BIOLOGY
Volume 36, Issue 1, Pages 20-31Publisher
AMER THORACIC SOC
DOI: 10.1165/rcmb.2006-0018OC
Keywords
TSG-6; l alpha l; tissue kallikrein; bikunin; airway
Funding
- NATIONAL HEART, LUNG, AND BLOOD INSTITUTE [R01HL073156, R01HL068992] Funding Source: NIH RePORTER
- NHLBI NIH HHS [HL-073156, HL-68992] Funding Source: Medline
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TSG-6 (the protein product of TNF-stimulated gene-6), an inflammation-associated protein, forms covalent complexes with heavy chains (HCs) from inter-alpha-inhibitor and pre-alpha-inhibitor and associates noncovalently with their common bikunin chain, potentiating the antiplasmin activity of this serine protease inhibitor. We show that TSG-6 and TSG-6(.)HC complexes are present in bronchoalveolar lavage fluid from patients with asthma and increase after allergen challenge. Immunodetection demonstrated elevated TSG-6 in the airway tissue and secretions of smokers. Experiments conducted in vitro with purified components revealed that bikunin.HC complexes (byproducts of TSG-6.HC formation) release bikunin. Immunoprecipitation revealed that bikunin accounts for a significant proportion of tissue kallikrein inhibition in bronchoalveolar lavage after allergen challenge but not in baseline conditions, confirming that bikunin in its free state, but not when associated with HCs, is a relevant protease inhibitor in airway secretions. In primary cultures of differentiated human airway epithelial and submucosal gland cells, TSG-6 is induced by TNF-alpha and IL-1 beta, which suggests that these cells are responsible for TSG-6 release in vivo. Bikunin and HC3 (i.e., pre-alpha-inhibitor) were also induced by TNF-alpha in primary cultures. Our results suggest that TSG-6 may play an important protective role in bronchial epithelium by increasing the antiprotease screen on the airway lumen.
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